The present invention relates to improvements in the electrodeposition of zinc from aqueous, acid plating baths. The use of polyamines as brightening agents in acid zinc plating baths is not new to the electroplating industry. U.S. Pat. No. 3,723,263 specifically discloses the combination of polyethylene imine and certain polyoxyethylene condensates. In a pending application filed with the U.S. Patent Office by the inventor herein, the use of aminated polyepichlorohydrin is disclosed as an acid zinc electroplating brightener along with polyoxyethylene condensates and aromatic aldehydes and ketones.
The bath formulations using polyethylene imine have a limiting factor in that at bath temperatures about 95.degree. F a severe loss of brightness of the electrodeposit occurs. Although the use of aminated polyepichlorohydrin has significantly minimized this high temperature deficiency, there exists another problem that is common to baths containing either the polyethylene imine or the aminated polyepichlorohydrin. When used with polyoxyethylene compounds and aromatic aldehydes and aromatic ketones, these polyamines produce quite dark electrodeposits upon extended electrolysis in the extreme low current-density areas of the parts of articles being plated. This situation can be corrected only by adding large amounts of expensive aldehydes and ketones. But even then, the problem is only temporarily overcome.
Since electroplaters often plate irregularly shaped articles with very low current-density areas, a bath that will consistently provide bright plate in these areas is extremely desirable.